low voltage calculation

[srengineer1]

When calculating voltage drop for a three phase service at a distance using ACSR cable, is voltage drop calculated using motor FLA or do you need to consider motor starting current?

 

[bob]

When calculating voltage drop for a three phase service at a distance using ACSR cable, is voltage drop calculated using motor FLA or do you need to consider motor starting current?

For standard VD calculations you use the FLA. If you are concerned about
voltage disturbance(flicker), use the starting amps.

 

[celtic]

I've never heard of ACSR being used for anything other than distribution .....how big is this motor?

 

[bsh]

if the motor is large, the cable is small or the distance is great you could have a motor starting problem. I had a clothes washer returned once because it wouldn't work (1/2 HP motor). Turned out they were plugging it into a 100 foot extension cord with # 18 conductor. If it is over 100 hp then starting voltage must be considered

 

[eric stromberg]

When calculating voltage drop for a three phase service at a distance using ACSR cable, is voltage drop calculated using motor FLA or do you need to consider motor starting current?

I like to see 80% voltage at the motor terminals during start-up. Not always possible, but a goal nonetheless. If LRA is assumed to be 6 times the FLA, then, if FLA voltage drop = 3%, LRA voltage drop = 18%. Check with the motor manufacturer to see what the terminal voltage should be during start-up.

 

[ramsy]

if FLA voltage drop = 3%, LRA voltage drop = 18%

Thanks for this helpful shortcut in the field, excellent information. However, I'm having a bit of trouble with Amps x 6 getting VD% x 6. It doesn't seem to be a linear calc at all. Try this yourself.